The extraction of liquid and gas hydrocarbons from subterranean deposits is performed by well drilling and pumping apparatus that has not changed substantially over the years. This apparatus usually includes a well casing and a well tubing that extends down inside the casing to a point below the normal level of oil in the casing. A reciprocating motor driven pump is usually provided inside the tubing. The pump has a plunger which is connected to a string of sucker rods that extends up through the tubing to connect with a polished rod which extends out of the ground and is attached to conventional oil well pumping structure such as a horse head walking beam and counterweights. The action of the reciprocating pump and the horse head walking beam cause the sucker rods and polished rod to lift a column of oil from a subterranean pool or deposit at the bottom of the well casing to the surface. A stuffing box or similar structure is typically located around the polished rod and contains packing or sealing material to prevent oil from being pumped out of the well casing and into the surrounding environment as the polished rod and sucker rods reciprocate to pump oil out of the well. Hydrocarbon-producing wells also include some type of delivery pipe or production line through which crude oil and well gas can be pumped to storage tanks.
The stuffing box or like structure that surrounds the polished rod usually contains one or more packing glands or sealing elements. The packing glands perform a sealing function and prevent oil from leaking out of the well around the polished rod. The packing glands and sealing materials available for this purpose are not indestructible and eventually are worn by chemical or physical contaminants, such as sand, and by the constant reciprocating motion of the polished rod. As a result, these structures will ultimately fail unless they are replaced first.
If a packing gland or sealing element fails, crude oil from the well may simply leak or spill around the polished rod or it may be forcibly blown out of the well. If an oil leak around the polished rod is not stopped promptly, the amount of leaking oil will quickly increase with the reciprocating action of the polished rod, especially if the polished rod is worn. As the leakage increases, the likelihood of damage to the polished rod and its associated structures also increases. Additionally, pumping action may also be affected, with the result that the effectiveness of the well in bringing oil to the surface is greatly decreased. If the leaking oil forcibly blows out of the well, damage to the surrounding environment could result.
In many oil fields the wells are spaced far apart over a large area and are not inspected frequently. Consequently, a failure of the polished rod sealing structures on one of these wells may not be discovered and corrected for some time after the leak actually occurred. If the sealing structures have failed to the point where oil is blown out of well, moreover, serious environmental damage could occur before it is discovered. Many jurisdictions impose heavy fines on oil well operators when the atmosphere, ground and/or water supply are polluted by hydrocarbon-producing well contaminants. Consequently, manual oil well inspections must be conducted at relatively short intervals to detect leaks as soon as possible after they begin.
Oil from the well may be used to lubricate the polished rod as it reciprocates axially upward and downward through the stuffing box and packing or sealing materials during well operation. If the flow of oil to the polished rod stops while the pump mechanism driving the polished rod is still operating, the polished rod will not be sufficiently lubricated. Unless the pump is stopped immediately, the polished rod and surrounding packing materials will be seriously damaged and require replacement. When oil wells are located far apart over a large area, the manual inspections typically performed by a single operator may not detect an oil flow stoppage early enough to prevent the substantial damage to the polished rod or associated structures which occurs when the well operates with too little or no lubrication of the polished rod.
The prior art has proposed various solutions to the aforementioned problems. U.S. Pat. No. 3,967,678 to Blackwell, for example, discloses a stuffing box control system for sensing the leakage of oil past the polished rod seals. In the event a leak is detected, it is corrected by adjusting the seals with a pressurized piston system. A pressure switching box including switches actuated by the hydrostatic head of the well fluid in a chamber separate from the polished rod and sealing structure is provided to control oil flow conditions in the stuffing box. However, the system described in this patent still requires an operator to monitor the piston system and correct any problems manually.
In U.S. Pat. No. 3,580,586 Burns discloses an inflatable packing glad to prevent the leakage of crude oil around the well polished rod which automatically maintains a predetermined optimum pressure of a packing member against the polished rod. This pressure, which may be amplified by well pressure, is exerted on the outer periphery of the packing member so that wear on the inner peripheral portion of the packing member in contact with the polished rod will not result in oil leaking around the polished rod. While this system does minimize the leakage of crude oil around the polished rod by maintaining a seal when the packing member is worn, it also has its limitations. In particular, adequate lubrication of the polished rod may not always be maintained.
U.S. Pat. No. 4,917,190 to Coppedge and U.S. Pat. No. 2,674,474 to Lister disclose, respectively, a system for containing an oil well blowout in the event of a failure of the packing gland and a system for maintaining a supply of lubrication fluid for the polished rod if the flow of oil from the well stops while the pump is still operating. The Coppedge system, however, still relies on manual inspection to ensure that it is functioning properly. The Lister system is limited to supplying lubricant to the polished rod and does not address the problem of oil leakage around the polished rod.
The prior art, therefore, has failed to disclose a sealing system for a hydrocarbon-producing well which simultaneously prevents the leakage of crude oil around the polished rod while providing sufficient oil to lubricate the polished rod during well operation. The prior art has further failed to provide a sealing system for a hydrocarbon-producing well which employs gas from the well casing to perform the primary sealing function.